Blindsight in action: what can the different sub-types of blindsight tell us about the control of visually guided...

Blindsight broadly refers to the paradoxical neurological condition where patients with a visual field defect due to a cortical lesion nevertheless demonstrate implicit residual visual sensitivity within their field cut. The aim of this paper is twofold. First, through a selective review of the blindsight literature we propose a new taxonomy for the subtypes of residual abilities described in blindsight. Those patients able to accurately act upon blind field stimuli (e.g. by pointing or saccading towards them) are classified as having 'action-blindsight', those whose residual functions can be said to rely to some extent upon attentive processing of blind field stimuli are classified as demonstrating 'attention-blindsight', while finally, patients who have somewhat accurate perceptual judgements for blind field stimuli despite a complete lack of any conscious percept, are classified as having 'agnosopsia'--literally meaning 'not knowing what one sees'. We also address the possible neurological substrates of these residual sensory processes. Our second aim was to investigate the most striking subtype of blindsight, action-blindsight. We review the data relevant to this subtype and the hypotheses proposed to account for it, before speculating on how action-blindsight may inform our normal models of visuomotor control.